message persists in queue

[Tobias.Wolf]

I'm using the following code to receive a message.
After a successful read I was expecting that the message is remove from the 
queue?!
But the message was still in the queue.
How can I read a message and remove it?

String result;
             ClientSession session = this.sessionFactory.createSession();
             try {
                    session.start();
                    ClientConsumer consumer = 
session.createConsumer(ACTIVE_MQ_SMTP_QUEUE);
                    ClientMessage message = consumer.receive();
                    result = message.getDataBuffer().readString();
                    message.acknowledge();
                    session.commit();
             } finally {
                    session.close();
             }